It is well known that electrical measuring instruments have very broad use in the electrical measuring art. Because of the large number of measurements which are made in regulating processes operated electrically there is need for large numbers of instruments. Because of the large number there is a premium on the smaller size instruments so that the instruments can be grouped to give readily available information to persons using the instruments.
Further, because of the very large number of such instruments which are used and the many purposes and applications in which they are employed, it is desirable that they be made at low cost and yet with high reliability and accuracy in performance.
This invention relates generally to the electrical instruments of the D'Arsonval type.
Instruments of the D'Arsonval type include a moving armature or coil assembly which is mounted for rotation through the field of a permanent magnet assembly. When the armature assembly is energized by means of a current flowing therethrough, the resulting magnetic fields interact to produce a torque which rotates the armature assembly relative to the permanent magnet assembly. An instrument pointer is generally connected to the movable armature assembly to yield a readout with respect to a faceplate or scale mounted behind the pointer as the torque is a function of the current magnitude.
One of the requirements for accuracy in instruments provided pursuant to the present invention is that they have a standard and reproducible reading from one instrument to another. In part this is dependent on having certain adjustments feasible in in the instrument and one such low-cost high-reliability and stable adjustment means is the subject of the present invention.